Electrical resistance unit



June 1929- w. E. DUERSTEN ELECTRICAL RESISTANCE UNIT Filed Aug. 29, 1924Patented June 4, 19 29.

UNITED STATES 1,715,824 PATENT- OFF-ICE.

WILLIAM E. DUERSTEN, F MILWAUKEE, WI SCONSIN, ASSIGNOR, BY MESNE ASSIGN-15. IENTS, TO GLOIBAR CORPORATION, OF NIAGARA. FALLS, NEW YORK, ACORPORA- men or new man.

ELECTRICAL RESISTANCE UNIT.

Application 111m August 29, 1924. Serial no. 7s4,a71.

The present invention relates in general'to electrically conductiveelements of the type known as resistance units, especially such a unitas is capable of producing in a commercial manner a relatively highdegree of heat on the passage of an electrical current through the unit,and also of maintaining itself in an efiicient mannerduring acommercially satisfactory life; and the invention is more particularlyconcerned with the production of such a resistance element provided withterminals of a character especiallyada-pted to withstand hightemperatures while connecting the unit in circuit in a mechanically andelectrically efiicient and generally satisfactory manner.

The problem of producing a commercially satisfactory terminal inconnection with a relatively inexpensive and efiicient electricalresistance element adapted to produce and withstand relatively hightemperatures, has been a considerable onein the past, especially'inconnection with resistance heating elements of what is knownin the artas the generally non-metallic class which have the characteristic ofbein able to produce and maintain relatively high temperatures with avery small degree of expansion. One certain ty e of commerciallysatisfactory resistor 0? this general class has been produced and hasgone into extended use, this resistor being constituted to aconsiderable extent of silicon carbide, with or without the addition ofone or more modifying substances; and the present invention findsconsiderable utility in connection with this type of resistance element.1

A great defect in connection with prior art devices of this characterhas been the failure to produce and maintain sufliciently intimatecontact between the metallic conductive terminal and the body of theresistor and to satisfactorily dissipate to the air or other surroundingmedium, theheat of the terminal; for as the resistor becomes heated,there is a tendency toward oxidation or burning or pitting of themetallic terminal with consequent final destruction thereof, due to theformation of minute arcs between the resistor-and '50 the terminal, witha consequent considerable increase in the resistance at the terminal.This results in a decrease in the effective voltage on the normal heatproducing portion of the resistor and, hence, an undesirable decrease inthe total heating effect of the remaintaining relatively hightemperatures,

the invention being more particularly concerned with such a resistanceelement constituted to a considerable extent'of silicon carbide as anessential ingredient, and wherein means are provided for forming anefiic5 cient electrical connection between the body of the resistanceelement and a line terminal and also constituting means for supportingthe resistance element, the general result including the provision of arelatively inexpensive and eflicient resistance unit adapted to producethe desired heating e'fl'ect and satisfactorily maintain itself undersevere operating conditions.

It is an object of this invention to provide an improved electricalresistance unit embodymg a terminal or connection element of 1mproveddesign and construction and adapted to withstand a considerable degreeof heat while maintaining an efiicient electrical connection andmechanical support for the resistance unit. It is a further object ofthis invention to provide an improved electrical resistance unitembodying a resistance element essentially constituted to a considerabledegree of silicon carbide or the like, and likewise embodying one ormore electrically conductive terminals attached to the resistanceelement, the unit as a whole constituting an inexpensive and efiicientresistance unit well adapted for producing and maintaining itself underhigh temperatures.

It is a further object of this invention to provide a terminal ofimproved design and construction for electrical resistance elements,more particularly of the heat generating type, which constitutes aneflicient electrical connection and mechanical support for theresistance element.

These and other objects and advantages are 1 obtained by the presentinvention, various novel features of which will be apparent from thedescription and drawings, disclosing embodiments of the invention, andwill be more 1 particularly pointed out in the claims.

In the accompanying drawings:

Figure 1 is a view in elevation, partly in section, of a resistanceelement embodying features of the present invention.

Figure 2 is a sectional view in theplane of the line IIII of Figure 1.

Figure 3 is a broken sectional view showing a modification of a featureof the invention disclosed in Figure 1. v

In accordance with the disclosure of the accompanying drawings, 10indicates a resistance element more particularly of the nonmctallic typeand essentially constituted to a considerable degree of silicon carbide.The

'cnds of the element 10 are provided with metallic terminals orconnectors embodying features of the present invention. As indicated,the terminal includes a hollow element or cap 12 having a central bore,the tubularwall of the bored portion being provided with externalthreads and longitudinally slotted at a plurality of points,-asindicated at 13, to provide spaced flexible fingers, The substantiallyclosed end portion 14 of the cap 12 has a central or axial threadedaperture 15 in which a line or circuitattaching screw 16 may be secured,the line terminal, whether it be in the form of one or more turns orlayers ofstrip or sheet metal, preferably aluminum foil, Wrapped aboutthe end of the bar, or it may be in the form of a dense coating ofaluminum or Monel metal deposited "inthe form'of minute particles aportion of which may impregnate the surface portion of the resistanceelement. In any case, the conductive coating 17 is of such a characterthat it is or may be forced into intimate engagement with the terminalportion of the resistance element which is of; a somewhat porousstructure.

lIVith the end of theresistance element and its conductive coatinginserted into the bore of the sleeve of the cap, a locking or clampindevice or collar 18 is applied to the exterior o the sleeve for thepurpose of clamping the V latter firmly upon and in intimate contactwith the resistance element.

The desired looking or clampin effect is preferably secured by having te outer threaded wall of the sleeve portion of the ca 12 somewhattapered toward its inner en thatis, toward the middle of the resistanceelement, and providing a clamping element or nut 18 having an internalthread tapered to poi-respond to the taper of the cap, the clampingelement being threaded onto the outer wall of the cap irom the inner endthereof.

As this clamping or locking element is threaded or forced onto thesleeve of the cap 12 from the inner end thereof, it has theefie'ct ofpinching or contracting the spaced portions or fingers of the tubularportion 12, formed by the slots 13. into firm and rigid frictionalengagement with the terminal portion of the resistance element directlyor with the conductive coating, where the latter is applied to suchterminal portion;

The inner end of the threaded clam ing element 18 is provided with anintegral auge 21 substantially perpendicular, or preferably slightlyinclined from a perpendicular, to the axis of the resistance element andcap, as indicated. This flange 21 is preferabl with spaced apertures 23or the. may serve for engagement by a tool for forcing the locking orclamping element into operative position on the tubular portion of thecap 12. As shown at the right in Figure 1, this flange extends towardthe middle of the resistance element, while at the left in this figure,the flange 21 extends away from the middle of the resistance element. Ineither case, the flange constitutes a shield for protecting the heatedportion of the resistance element from accidental contact with externalobjects, and alsoa heat conducting shield which dissipates heat'from thebody portion of the cap, and thus assists in preventing over heating ofthe end and body portion ofthe terminal; The cap 12 provided e which iand the clamping element 18 with its integral flange-like shield may beof any material having the desired conductivity and which does notreadily oxidize at the normal operating temperatures of the terminal;and'the radiating surface of the terminal as a whole should be such asto keep its operating temperature belowared heat. g

In the modification shown in Figure 3,'the end of the resistance element10'is provided with corrugations, preferably in the form of screwthreads, andthe bore of the terminal cap 12 is provided with internalthreads for engagement with the-threads formed ou-the I end of theresistance element, permitting v.

screwing the cap to operative position onthe terminal portion of theresistance element.

The other features may be the same as shown in Figure 1'. The pitch ofthe threads formed i f on the end of the resistance element may beopposite to that of thethreads formed on the exterior of the terminalcap, toassist in look ing the cap. on the end of the'resistanceelementas .the clamping element 18-isforced into operative position on thethreaded outer surface of the sleeve portion of the cap A conductivecoating 17 of the t pe. described in connection wit Figure l is likewiseapplied to the corrugated or threaded end of the resistance elementprior to disposing the lat- .ter in operative'position within the boreof the terminal cap 12. The corrugationsgor of the cap 12 have theadded'funct ion of providing additional surface contact between the pand threaded clamping collar surrounding terminal portion of the.resistance element and the terminal ca 12 and the intermediateconductive coating 17. The resistance element is preferably formed froma mixture containing silicon carbide as an essential element, with orwithout one or more metallic modifying substances, and molded and bakedand burnt or fired. at a high temperature to produce aheat-hardenedresistance element' of the desired mechanical and electrlcalcharacteristics.

With a conductive coating of the character described applied to the endof the resistance element and the latter disposed within the bore of thesleeve-like portion of terminal cap 12 and the cap clamped or locked inoperative position, an efiicient mechanical and electrical connection ofthe parts is secured.

lVith the complete resistance unit operatively connected to a supplyline through theconnection screws 16, the effect of a high degree ofheat producedin the resistance element may be to weld or alloy orintimately unite,

the metallic coating 17 to the associated parts of the resistance unit.In general, the electrical and mechanical connection secured ashereinabove described is of a very efiicient character, even while theresistance unit is operating at relatively high temperature.

It should be understood that the inven-' tion claimed is not limited tothe exact details of construction and design shown and described herein,for it will be apparent that obvious modifications will occur to personsskilled in this particular art.

It is claimed and desired to secure by Letters Patent: 4

1. An electrical resistance heating unit, comprising a self-sustainingresistance heating element capable of producing and maintaining itselfat high operating'temperatures, a conductive terminal for Sflld' heatingelem'e'nt comprising an externally tapered and threaded contractilesleeve portion at one end surrounding a terminal portion of said heatingelement and a substantially ri id-portio'n at the other end, and aninterna ly tapered and adjustable upon said contractile sleeve portionand adapted to force and hold said sleeve in intimate engagement withsaid terminal portion of the heating element, said clamping collar beingprovided adjacent its inner end with an external flange-like shieldinclined away from said inner end.

2. An electrical resistance heating unit, comprisng a self-sustainingresistance heating element capable of producing and maintaining itselfat high operating temperatures and having a terminal portion ofcorrugated or irregular surface outline, a conductive terminal having acontractible sleeve-like portion of correspondingly irregular outline tointimatelyenga-ge with said terminal portion of the heating element whenthe latter is disposed within said sleeve, and annular clamping meanscooperative with the exterior of said sleeve for causing said sleeve toforcibly grip and intimately engage said terminal portion of the heatingelement, said clamping means having at its end nearest the center of theheating element and inclined away therefrom a flange-like shield adaptedto dissipate heat from the body portion of said conductive terminal.

3. An electrical resistance heating unit, comprising a self-sustaininresistance heating element capable of pro ucing and maintaining itselfat high operating temperatures and having a terminal portion providedWithscrew threads, a conductive terminal having a cont'ractiblesleeve-likeportion surrounding said terminal portion of the heatingelement, said conductive terminal being provideclwith screw threads incooperative intimate engagement with the screw threads on said terminalportion of the heating element, and annular clamping means cooperativewith the exterior of said, sleeve for causing said sleeve tov forciblygrip and intimately engage said terminal portion of the heating element,said clamping means having at its end nearest the center of the heatingelement and inclined away therefrom a flangelike shield adapted todissipate heat from ,the body portion of said conductive terminal.

In witness whereof I affix my signature.

hereto.

- DUERsTEm

